1. Field of the Invention
The invention relates to intermediate polyol blends, to resin prepolymer compositions incorporating such polyol blends, to cellular polyurethane-polyisocyanurate polymers made from such polyol blends and such resin compositions by reaction thereof with isocyanates, and to processes for the preparation of such respective blends, compositions, and cellular polymers.
2. Description of the Prior Art
Cellular polyurethane and polyisocyanurate polymers are well known in the art particularly for use in various types of thermal insulating applications. Such polymers are manufactured by reacting polyfunctional organic isocyanates with polyfunctional compounds containing free hydroxyl groups (e.g., polyols) in the presence of a blowing agent and (usually) a catalyst.
Because of the relatively high cost of polyols useful in making cellular polymers, efforts have been heretofore made to find polyols adapted for chemical conversion into such cellular polymers which are as low cost as possible. Because of a tendency for lower cost polyols to produce product foams of less than desired properties, it has become commonplace to prepare and utilize blends of different polyols for reaction with organic polyisocyanates to produce product foams having the desired combinations of properties. Thus, through the use of polyol blends, product foam problems can be avoided, such as lack of uniform core and adjacent substrate, excessive foam friability, and the like. The polyol blends typically are compounded with other additives including fluorocarbon blowing agents to produce so-called resin prepolymer blend compositions which are ready for admixture with (and reaction with) organic isocyanates to produce cellular polyurethane-polyisocyanurate polymers by the reaction that results.
The blending of aromatic polyester polyols, including aromatic polyester diols, can result in compounding problems and in product quality problems. For example, when fluorocarbon blowing agents are employed in resin blends containing aromatic polyester polyols, incompatibility problems may arise between the polyol blend or system and the fluorocarbon blowing agent. Similar problems can arise between such a polyol blend and the isocyanate catalyst system used for achieving a desired reaction between such polyols and isocyanates.
Because of blendability and product foam quality considerations, there are not many commercially suitable low cost polyester polyols available. One class of such polyols which has heretofore been employed in this art comprises reaction products of a low molecular weight polyether polyol, such as diethylene glycol, with poly (carbomethoxy-substituted) diphenyls and benzyl esters. Such products are available commercially under the trademarks "Terates" from Hercules Inc. and "Urol 11" from UCT, Inc. Such diphenyl and benzyl ester diethylene glycol products are commercially used at rates ranging up to about 15 to 20 weight percent of a polyol blend (based on total blend weight) in making cellular products in the rigid foam urethane industry.
There remains in this art a need for new and low cost polyester polyol blends which can be incorporated into resin prepolymer compositions for use in the manufacture of cellular polyurethane-polyisocyanurate polymers of commercial quality.